Biodegradable Piezoelectric Scaffold for Bone Regeneration Reconstruction of large bone fractures and defects remains a big challenge in orthopaedic surgery. Replacement auto- or allo-grafts usually suffer from the problems of limited supply, donor site morbidity, infection or/and immune-rejection. Regenerative engineering strategies, employing a combination of biomaterial scaffolds, stem/osteogenic cells and growth factors/small molecules, has therefore emerged as an important area. Although bone growth factors and small molecules are powerful, many of their toxic side-effects demand for a new approach to stimulate bone growth. Electrical stimulation (ES) is an excellent alternative and many electrical stimulators have been used to treat bone fractures. However, the electrical devices still struggle with limitations; while external stimulators are not very effective, implanted devices rely on toxic and non- degradable batteries, requiring invasive removal surgery. Piezoelectric materials, a group of ?smart? materials which can generate electricity under applied force, might offer compelling battery-less stimulators to electrically stimulate bone growth. Bone is also piezoelectric in nature. Under deformation, bone generates surface charge, which drives the tissue to grow against the applied force. A piezoelectric scaffold can therefore mimic natural bone in receiving mechanical loading to induce bone growth and regeneration. Here we propose for the first time a novel biodegradable and biocompatible scaffold of piezoelectric nanofibers of PLLA (Poly-L-lactide), which will be seeded with stem cells and subjected to acoustic pressure from ultrasound, to generate useful electrical charge for enhanced bone regeneration. We will assemble multiple layers of electrospun piezoelectric PLLA nanofiber films and employ adipose stem cells (ASCs) to construct the 3D piezoelectric scaffold. Accordingly, the project has two main specific aims; Aim 1 is to assess osteogenesis from ASCs seeded on the 3D biodegradable piezoelectric PLLA nanofiber scaffold under stimulation of acoustic pressure in vitro. And Aim 2 is to demonstrate the use of our constructed scaffold to heal critical-sized calvarial/skull defects in mice under stimulation of acoustic pressure. Milestone: The milestone of this project after 1 year is to find out suitable acoustic stimulation and demonstrate an enhanced osteogenesis from the stem-cells, seeded on our piezoelectric PLLA scaffold, in vitro. After 2 years, the milestone of this project is to demonstrate a significant bone ingrowth on implanted piezoelectric PLLA scaffolds to heal the calvarial defects in mice. As electrical stimulation is applicable to versatile tissues (e.g. nerve, muscle, skin, cartilage etc.), we anticipate the proposed scaffold will become a platform to construct different engineered tissues with an enhanced regenerative capability.